Fusion welding fittings with weld bead cover

ABSTRACT

A fitting for use in fusion welding mating thermoplastic components includes a weld bead chamber to capture and conceal a bead formed as a result of the fusion weld. The weld bead chamber integrates the bead into the fitting so that the joined parts have a finished look without mechanical polishing or grinding of the completed piece. A stop ledge included in the weld bead chamber prevents over insertion of a pipe or other component into the fitting. A view window in the fitting permits inspection of the finished bead.

BACKGROUND OF THE INVENTION

The present invention relates generally to the attachment of pipes andthermoplastic fitting components by means of fusion welding. Moreparticularly, the invention relates to improved fittings for joiningthermoplastic components.

A number of companies have developed plastic welding equipment whichutilizes specialized fitting components to join thermoplastic piping.Plastic welding can be categorized into three types: fusion welding, IRButt Fusion, and Bead and Crevice Free welding. Fusion welding is usedfor high purity installations of thermoplastic piping. Thermoplasticpiping has grown in industrial usage because of its compatibility withchemicals, its non-corrosive nature, ease of installation, long life,and its smooth internal surfaces. These features of thermoplastic pipingmake it ideal for high purity applications.

Standard fusion welding involves the heat fusion of a pipe into a femalesocket fitting. Bonding is achieved by heating the mating surfaces ofthe pipe end and of the fitting to a temperature above the melt point ofthe material. The heated parts are then engaged and held together untilfused. Fusion occurs when the parts are cooled to below the melt pointof the material.

Heating is typically achieved through conductive means via an electricheater that reaches temperatures in the regions of 500° F.±10° (or 260°C.). With the appropriate time, the pipe and fitting surfaces which comein direct contact with the heating tool will melt. The parts are thencarefully removed from the heating tool and quickly pushed togetherthereby fusing the two parts together. Fusion welding is also used forwelding a pipe or fitting to a plate in the same manner described aboveexcept the plate replaces the female socket.

The relationship between the outside diameter of the pipe and the boreof the fitting or plate is critical for successful fusion welding.Interference is essential when the hot surfaces are mated together. Acarefully designed interference fit of the heated mating parts providesconsistency of joining. It also results in the appearance of a weld beadas excess melted material is “scraped” off one of the surfaces. Thisweld bead is undesirable to some users because of its fabricated,unfinished look; and because of the potential for the weld to entrapairborne particles that can be embedded in the material while in amelted state.

The weld bead provides insight to whether the heat fusion joint wasproperly made. Ideally a double weld should be present and it should notbe large in size. As stated above, one disadvantage to the weld bead isthat it gives the joint a fabricated appearance. Another disadvantage isthat dark spots may appear on the areas of the weld bead due to normalheating or particles which may have been captured when the material wasin a melted state. Some manufacturers that use heat fusion to produceproducts machine the weld bead in order to create a more professionalmolded look. This adds an additional step to the manufacturing process.

Accordingly, there is a need for an improved fitting that integrates theweld bead into the fitting resulting in the final product having a morefinished look. Additionally, an improved fitting that will prevent thecommon mistake of over inserting a mated component by providing anadditional stop to the fitting is needed. Moreover, there is a need forreducing the manufacturing steps involved in heat fusion by eliminatingremoval of the weld bead through machining. The present inventionfulfills these needs and provides other related advantages.

SUMMARY OF THE INVENTION

The present invention relates to a fitting for use in fusion welding ofmating thermoplastic components. The fitting comprises a body defining apassageway therethrough and having a weld bead chamber disposed about aportion of the body. The weld bead chamber is configured to receiveexcess thermoplastic material resulting from a fusion weld joining thebody to a mating thermoplastic component. The mating thermoplasticcomponent may be a pipe or a hole in a plate, a wall, a vessel, apressurized chamber, etc. The fitting is preferably cylindrical inshape, but may also be triangular, square, rectangular, etc.

In one preferred embodiment, the fitting includes a threaded connectoron an end opposite the weld bead chamber. The body of the fittingadjacent to the weld bead chamber is configured for interference fitreception within the mating thermoplastic component. The weld beadchamber includes a stop ledge to prevent over insertion of the fittinginto the mating thermoplastic component.

In another preferred embodiment, the fitting has a second weld beadchamber adjacent to an end of the body opposite the first weld beadchamber. As in the first embodiment, the body adjacent to either weldbead chamber is configured for interference fit reception with a matingthermoplastic component. Again, the weld bead chamber includes a stopledge to prevent over insertion of the pipe into the fitting.

The body of the fitting is made from a heat fusible thermoplasticmaterial, such as, polypropylene, polyethylene, polybutylene,polyvinylidene fluoride, or Teflon.

The weld bead chamber includes a window to view the excess thermoplasticmaterial that results from the interference fit between the fitting andthe mating thermoplastic component.

The body of the fitting may include a bend between a first end and asecond end of the body. In addition, the body of the fitting may includea T-junction between a first end and a second end of the body, where athird opening of the T-junction includes a third weld bead chamber.

A method for fusion welding a fitting to a mating thermoplasticcomponent comprises the step of heating mating surfaces of the fittingand the mating thermoplastic component to a temperature above the meltpoint of each, typically at least 500° F. Next, surfaces of the fittingand the mating thermoplastic component configured for an interferencefit are engaged until a stop ledge in the weld bead chamber until themating thermoplastic component engages a stop ledge. Excessthermoplastic material removed from either the fitting or the matingthermoplastic component as a result of the interference fit is capturedin the weld bead chamber. The engaged parts are then cooled. The excessthermoplastic material may be inspected through the window in the weldbead chamber.

Other features and advantages of the present invention will becomeapparent from the following more detailed description, taken inconnection with the accompanying drawings which illustrate, by way ofexample, the principles of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate the invention. In such drawings:

FIG. 1 is an elevational view of a fitting of the present inventionshowing an internal passageway in dashed lines;

FIG. 2 is a sectional view taken generally along line 2-2 in FIG. 1;

FIG. 3 is a sectional view similar to FIG. 2, additionally depicting thefitting mated to a pipe;

FIG. 4 is a sectional view taken generally along line 4-4 in FIG. 1;

FIG. 5 is a perspective view of the fitting of FIG. 1, fusion welded toa plate;

FIG. 6 is an elevational view of the assembly of FIG. 5;

FIG. 7 is a cross-sectional view generally taken along line 7-7 in FIG.6;

FIG. 8 is a side view of an alternate embodiment of the fitting of thepresent invention welded to two pipes;

FIG. 9 is a sectional view generally taken along line 9-9 in FIG. 8;

FIG. 10 is a sectional view of the fitting of FIGS. 8 and 9;

FIG. 11 is a sectional view of a T-shaped fitting embodying the presentinvention; and

FIG. 12 is a sectional view of an elbow fitting embodying the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is directed to improved fittings to be used infusion welding of mating thermoplastic components. Standard fusionwelding results in a weld bead which is undesirable to some usersbecause of its fabricated, unfinished look, and because of the potentialfor the weld to entrap air borne particles that can be embedded in thematerial while in a melted state. The improved fittings of the presentinvention allow manufacturers to continue using fusion welding in theirmanufacturing steps while giving their products a more finished andinjection-molded look by integrating the weld bead, and helping preventthe common mistake of over insertion by providing an additional stop inthe fitting. It also reduces manufacturing steps by eliminating removalof the weld bead through machining which some companies current performon their products.

As illustrated in FIGS. 1 through 7, an improved fitting 20 embodyingthe present invention comprises a body 22 having a weld bead chamber 24.A passageway 26 runs through the body 22 and provides physicalcommunication between adjoining thermoplastic components, i.e., pipes,vessels, etc., mated to the fitting 20. The body 22 and passageway 26are preferably cylindrical but may take the form of any shape that iscompatible with the shape of a mated thermoplastic component, i.e.,triangular, square, rectangular, etc. The fitting 20 also includes athreaded coupling 28 which can receive a cap, flare tube and nut,compression connection with a split ring, ferrule, and nut, or othertype of connector (not shown).

The weld bead chamber 24 is preferably a continuous annular ringprovided on the outer perimeter of the body 22 and oriented toward anend of the body. However, it may be a discontinuous annular ring, butsuch construction will not completely integrate and conceal the weldbead. A stop ledge 30 is included in the weld bead chamber 24 to preventover insertion of the fitting 20 and mated thermoplastic component,i.e., a pipe 32 or a wall/plate 34. The function of the stop ledge 30will be discussed more fully below.

The fitting 20 of is typically joined by fusion welding to either a pipe32 or a plate or wall of a vessel 34. When joined to a pipe 32, the endof the fitting 20 adjacent to the weld bead chamber 24 is inserted intothe pipe 32. The pipe 32 with which the fitting 20 is mated may be aregular straight pipe or may comprise a multi-junction pipe, i.e., aT-shaped junction, which can be joined to multiple fittings 20.

The diameters of the fitting 20 and the mating pipe 32 are chosen so asto create and interference fit. This means that the outer diameter ofthe fitting 20 is so close to the inner diameter of the pipe 32 thatthere is substantial surface contact around the perimeter of the fitting20. This carefully designed interference fit of the heated mating partsprovides consistency of jointing.

Prior to insertion of the fitting 20 into the mating pipe 32, the outersurface of the fitting 20 and the inner surface of the pipe 32 areheated to a temperature above the respective melting points of each. Theheated surfaces of the fitting 20 and pipe 32 are then engaged and heldtogether until cool and fused.

The interference fit results in a portion of the surface of the fitting20 being “scraped” off and accumulating as a bead 36 around the end ofthe pipe 32. In prior fusion welding processes, this bead 36 would bemachined off for a more finished appearance. However, in the presentinvention, the weld bead chamber 24 on the fitting 20 conceals the bead36 so that it does not need to be machined off.

In addition, the weld bead chamber 24 includes a stop ledge 30 (FIG. 2)within the weld bead chamber 24 to prevent over insertion of the fitting20 into the pipe 32. The stop ledge 30 presents a surface against whichthe end of the mating pipe 32 abuts to prevent insertion of the fitting20 beyond that point of abutment. This stop ledge 30 is positioned fromthe end of the fitting 20 so that there is a minimum amount of surfacecontact between the fitting 20 and the pipe 32 to ensure a strong fusionweld. In cases where the outside diameter of pipe 32 is too large forthe end to fit within the weld bead chamber 24, or when it is morepractical to simplify the fitting, then a stop ledge edge 31 willprevent over insertion.

The fitting 20 also includes one or more view windows 38 to inspect thequality of the bead 36 after the parts are mated. The appearance of thebead 36 correlates to the quality of the fusion weld between the matedparts. It is important that one be able to inspect the bead 36 todetermine the quality of the fusion weld before using the mated pieces.

When the fitting 20 is fusion welded to a plate or wall of a vessel 34,the end of the fitting 20 is inserted into a hole in the plate or wall34. The manner in which these pieces are mated is nearly as describedabove: the respective diameters are close enough to create aninterference fit; the mating surfaces are heated to above the meltpoint; the heated surfaces are mated; excess surface material is“scraped” off the surface of the fitting 20 and accumulated as a bead 36around the surface of the plate or wall 34; the parts cool and fusionweld together; the bead 36 is covered by the weld bead chamber 24. Onedifference involves that part of the fitting 20 that acts as the stopledge 30. When welding the fitting 20 to a plate or wall 34, the stopledge is an edge 31 (FIG. 7) of the weld bead chamber 24 rather than asurface inside the weld bead chamber 24 as described above.

FIGS. 8 through 12 depict another preferred embodiment of the presentinvention for coupling together opposed ends of two pipes by fusionwelding (or more then two as in a tee). In this embodiment, the fitting40 comprises a body 42 including a passageway 44 therethrough. Thisfitting 40 includes a first weld bead chamber 46 at a first end and asecond weld bead chamber 48 at a second end. These weld bead chambers46, 48 comprise continuous annular grooves around the inside diameter ofthe passageway 44. The weld bead chambers 46, 48 may be discontinuousannular grooves, but such construction will not completely integrate andconceal the weld bead. The fitting 40 includes a stop ledge 50 adjacentto each weld bead chamber 46, 48 to perform a similar function asdescribed above. In this embodiment, the stop ledge 50 is included inthe passageway 44.

The diameters at each extreme end 52 of the fitting 40 are larger thanthe diameter of the passageway 44 but smaller then the diameter of theweld bead chambers 46, 48. Because the diameters at each extreme end 52of the fitting 40 are larger, they will not contact the heater and theextreme end material will not melt. The extreme end 52 diameter issmaller then the diameter of the weld bead chambers 46, 48 to provide ameans to keep the bead 52 (discussed below) within the chambers 46, 48.

The fitting 40 is designed to receive a pipe 54 within each end of thefitting 40. For the joining of one pipe 54 to a first end of the fitting40, the inner diameter of the passageway 44 is closely matched to theouter diameter of the pipe 54 so as to create an interference fitbetween the two parts. The mating surfaces are then heated and the pipe54 is inserted into the fitting 40. The interference fit results inexcess material being scraped off of the heated surfaces and forming abead 56 which accumulates in the weld bead chamber 46. The stop ledge 50prevents over insertion of the pipe 54 into the fitting 40 by abuttingagainst the end of the pipe 54. Again, a view window 58 permitsinspection of the bead 56.

This configuration may be formed integral with a member such as a valvebody, a tee (FIG. 11), an elbow (FIG. 12), or a pipe connector (FIGS.8-10). The pipe connector style fitting 40 has been described above. Asshown in FIG. 11, the fitting 40 may include more than two openings andhence, more than two weld bead chambers 46, 48, 60. When more than twopipes 54 are mated to this fitting 40, a corresponding number of weldbead chambers 46, 48, 60 are provided. Similarly, as shown in FIG. 12, afitting 40 may include a bend or elbow to allow for an angled mating ofpipes 50.

The fittings 20, 40 and their mated components, 32, 34, 54 arepreferably manufactured from heat fusible thermoplastic materials. Suchheat fusible thermoplastic preferably includes Polypropylene (PP),Polyethylene, Polybutylene, Polyvinylidene Fluoride (PVDF), Teflons suchas PFA and FEP, and other materials. Fusion welding has becomeestablished in industry as a primary joining system for small and mediumsizes of Polyvinylidene Fluoride (PVDF) and polypropylene pipe (PP).Fusion welding is typically used for sizes from ½″ up to 100 mm or 4″piping diameter. Heating of the components is typically achieved throughconductive means via an electric heater that reaches temperatures in theregions of 500° F.±10° (or 260° C.). With the appropriate time, thesurfaces of the fittings 20, 40 and mating components 32, 34, 54 whichcome in direct contact with the heating tool will melt. The parts arethen carefully removed from the heating tool and quickly pushed togetherthereby fusing the two parts together.

Although various embodiments have been described in detail for purposesof illustration, various modifications may be made without departingfrom the scope and spirit of the invention.

What is claimed is:
 1. A fitting for use in the fusion welding of matingthermoplastic components, comprising: a body defining a passagewaytherethrough; and a weld bead chamber disposed about a portion of thebody to receive excess thermoplastic material resulting from a fusionweld joining the body to a mating thermoplastic component, wherein theweld bead chamber includes a stop ledge to prevent over insertion of thefitting, and wherein a portion of the body adjacent to the weld beadchamber is configured for interference fit reception with athermoplastic pipe or an opening in a thermoplastic surface.
 2. Thefitting of claim 1, wherein the body is cylindrical in shape and has athreaded coupling adjacent to an end of the body opposite the weld beadchamber.
 3. The fitting of claim 1, wherein the fitting has a secondweld bead chamber adjacent to an end of the body opposite the first weldbead chamber.
 4. The fitting of claim 3, wherein a portion of the bodyadjacent to either weld bead chamber is configured for interference fitreception around a thermoplastic pipe, and wherein either weld beadchamber includes a stop ledge to prevent over insertion of a pipe intothe fitting.
 5. The fitting of claim 1, wherein the body comprises aheat fusible thermoplastic.
 6. The fitting of claim 5, wherein the bodyis comprised of a polypropylene, polyethylene, polybutylene,polyvinylidene fluoride, or Teflon material.
 7. The fitting of claim 1,wherein the fitting includes a window for viewing excess thermoplasticmaterial after the body is fusion welded to the mating thermoplasticcomponent.
 8. The fitting of claim 1, wherein the body includes a bendbetween a first end and a second end of the body.
 9. The fitting ofclaim 1, wherein the body includes a T-junction between a first end anda second end of the body, and wherein the T-junction includes a thirdweld bead chamber.
 10. A fitting for use in the fusion welding of matingthermoplastic components, comprising: a body defining a passagewaytherethrough and configured for interference fit reception around amating thermoplastic component; a weld bead chamber disposed about aportion of the body to receive excess thermoplastic material resultingfrom a fusion weld joining the body to the mating thermoplasticcomponent; and a stop ledge positioned from an end of the fitting andformed adjacent the weld bead chamber to prevent over insertion of thefitting or the mating thermoplastic component; wherein a diameter of thestop ledge is greater than a diameter of the weld bead chamber, and thediameter of the weld bead chamber is greater than a diameter of the bodypassageway; and wherein excess thermoplastic material removed fromeither the fitting or the mating thermoplastic component is captured andconcealed in the weld bead chamber.
 11. The fitting of claim 10, whereinthe body is cylindrical in shape and has a threaded coupling adjacent toan end of the body opposite the weld bead chamber.
 12. The fitting ofclaim 10, wherein a portion of the body adjacent to the weld beadchamber is configured for interference fit reception with athermoplastic pipe or an opening in a thermoplastic surface.
 13. Thefitting of claim 10, wherein the fitting has a second weld bead chamberadjacent to an end of the body opposite the first weld bead chamber. 14.The fitting of claim 13, wherein a portion of the body adjacent toeither weld bead chamber is configured for interference fit receptionaround the mating thermoplastic component, and wherein either weld beadchamber includes a stop ledge to prevent over insertion of a pipe intothe fitting.
 15. The fitting of claim 10, wherein the body comprises aheat fusible thermoplastic.
 16. The fitting of claim 15, wherein thebody is comprised of a polypropylene, polyethylene, polybutylene,polyvinylidene fluoride, or Teflon material.
 17. The fitting of claim10, wherein the fitting includes a window for viewing excessthermoplastic material after the body is fusion welded to the matingthermoplastic component.
 18. The fitting of claim 10, wherein the bodyincludes a bend between a first end and a second end of the body. 19.The fitting of claim 10, wherein the body includes a T-junction betweena first end and a second end of the body, and wherein the T-junctionincludes a third weld bead chamber.